<!DOCTYPE html>
<html>
<head>
    <title>主题示例</title>
    <style>
        .light { background: white; color: black; }
        .dark { background: black; color: white; }
    </style>
</head>
<body class="light">
<h1>主题切换示例</h1>
<button onclick="document.body.className='dark'">深色模式</button>
<button onclick="document.body.className='light'">浅色模式</button>
</body>
</html>